The long-term objective of this research is to better understand the biochemical, genetic and physiological mechanisms of aging and age related changes in man through investigation of similar biochemical and physiological changes in the domestic dog, Canis familiaris. With life span in the American population nearly doubling in the last century, it is becoming of greater importance both economically and socially, to understand the biological mechanisms allowing for healthy old age. Through a mechanistic understanding of the biological processes contributing to old age, methodology can be derived by which the increasingly older population of Americans is also an increasingly healthier population. Towards the goal of understanding the genetic and biochemical mechanisms promoting healthy longevity, this application proposes the utilization of the domestic dog for investigation of the free radical theory of aging. The working hypothesis is that oxidative stress contributes considerably to the aging process and specific mechanisms associated with aging and longevity can be determined by investigating the cellular and genetic differences between breeds with naturally diverse life span. The primary objective is to investigate the working hypothesis by examining the mechanisms through which oxidative stress may influence longevity in the dog. Because oxidative stressors have been demonstrated to affect longevity in other organisms (Kapahi et al, 1999;Campisi et al., 2001), it will be vital to elucidate the effects of the stressors in a mammalian system whose lifetime of medical care closely resembles the human's (Parker et al., 2004), yet has a life span significantly shorter than the human. Specifically, we determine 1) if oxidative stress levels are correlated to longevity within C. familiaris, 2) the level of gene expression of primary enzymes associated with diminishing cellular stress. Establishing this strong basis of knowledge regarding stress resistance in primary canine fibroblasts sets the stage for future more detailed investigations into the additional parameters within each biochemical pathway determined associated with longevity. Further, owner contact for the dogs is maintained, facilitating longitudinal data.